Method of assembly for gas turbine fan drive gear system

ABSTRACT

A method of assembling an epicyclic gear train comprises the steps of providing a unitary carrier having a central axis that includes spaced apart walls and circumferentially spaced connecting structure defining spaced apart apertures provided at an outer circumference of the carrier. Gear pockets are provided between the walls and extend to the apertures. A central opening is in at least one of the walls. A plurality of intermediate gears are inserted through the central opening and move the intermediate gears radially outwardly into the gear pockets to extend into the apertures. A sun gear is inserted through the central opening. The plurality of intermediate gears is moved radially inwardly to engage the sun gear.

This application is a divisional of U.S. patent application Ser. No.13/975,635, filed Aug. 26, 2013, which is a divisional of U.S. patentapplication Ser. No. 13/629,834, filed Sep. 28, 2012, now U.S. Pat. No.8,667,688, which is a continuation-in-part of U.S. patent applicationSer. No. 12/718,436, filed Mar. 5, 2010, now U.S. Pat. No. 8,276,275,which is a divisional application of U.S. patent application Ser. No.11/481,112, filed on Jul. 5, 2006, now U.S. Pat. No. 7,704,178.

BACKGROUND OF THE INVENTION

This invention relates to assembling an epicyclic gear train employed todrive a turbo fan.

Gas turbine engines may employ an epicyclic gear train connected to aturbine section of the engine, which is used to drive the turbo fan. Ina typical epicyclic gear train, a sun gear receives rotational inputfrom a turbine shaft through a compressor shaft. A carrier supportsintermediate gears that surround and mesh with the sun gear. A ring gearsurrounds and meshes with the intermediate gears. In arrangements inwhich the carrier is fixed against rotation, the intermediate gears arereferred to as “star” gears and the ring gear is coupled to an outputshaft that supports the turbo fan. In arrangements in which the ringgear is fixed against rotation, the intermediate gears are referred toas “planetary” gears and the carrier is coupled to the output shaft thatsupports the turbo fan.

The housings are typically split along a central plane, and the geartrain can be assembled, with the carrier housing halves then beingbrought together and secured. For improved strength and rigidity, ascompared with a two-part housing, it is desirable for an epicyclic geartrain to have a unitary carrier housing.

SUMMARY OF THE INVENTION

In a featured embodiment, a method of assembling an epicyclic gear traincomprises the steps of providing a unitary carrier having a central axisthat includes spaced apart walls and circumferentially spaced connectingstructure defining spaced apart apertures provided at an outercircumference of the carrier. Gear pockets are provided between thewalls and extend to the apertures. A central opening is in at least oneof the walls. A plurality of intermediate gears are inserted through thecentral opening and move the intermediate gears radially outwardly intothe gear pockets to extend into the apertures. A sun gear is insertedthrough the central opening. The plurality of intermediate gears ismoved radially inwardly to engage the sun gear.

In another embodiment according to the previous embodiment, moving theplurality of intermediate gears radially inwardly to engage the sun gearoccurs after the sun gear is inserted through the central opening.

In another embodiment according to any of the previous embodiments,journal bearings are inserted within each of the intermediate gearsafter the sun gear is inserted through the central opening.

In another embodiment according to any of the previous embodiments, aring gear is subsequently placed on an outer periphery of the sun gearsto engage the sun gears.

In another embodiment according to any of the previous embodiments, thesun gear and the intermediate gears are each formed as a single gear,and the ring gear is formed as a two-part gear.

In another embodiment according to any of the previous embodiments, afirst ring gear half is first placed about the outer periphery of theintermediate gears, and a torque frame is then attached to the carrier.

In another embodiment according to any of the previous embodiments, asecond ring gear half is mounted to the outer periphery subsequent tothe torque frame being mounted to the carrier.

In another embodiment according to any of the previous embodiments, thetorque frame has a plurality of axially extending fingers that arereceived within slots in the carrier, at locations circumferentiallyintermediate locations of the intermediate gears. The first ring gearhalf is moved such that it does not block radially inwardly extendingapertures in a radially outer surface of the carrier. Pins are thenmoved into the apertures to lock the fingers within the slots, with thefirst ring gear half then being moved over the apertures.

In another embodiment according to any of the previous embodiments, thesecond ring gear half is placed on the intermediate gears subsequent tothe locking of the fingers within the slots.

In another featured embodiment, a method of mounting a gear train to atorque frame comprises providing a unitary carrier having a central axisthat includes spaced apart walls and circumferentially spaced connectingstructure defining mounts for interconnecting the walls. Spaced apartapertures are provided between the mounts at an outer circumference ofthe carrier. Gear pockets are provided between the walls. Mounts extendto the apertures, and a central opening in at least one of the walls. Aplurality of intermediate gears and a sun gear are inserted in thecarrier. A first ring gear half is placed about the outer periphery ofthe intermediate gears, and attach a torque frame to the carrier.

In another embodiment according to the previous embodiment, a secondring gear half is then mounted to the outer periphery subsequent to thetorque frame being mounted to the carrier.

In another embodiment according to any of the previous embodiments, thetorque frame has a plurality of axially extending fingers that arereceived within slots in the carrier, at locations circumferentiallyintermediate locations of the intermediate gears. The first ring gearhalf is moved such that it does not block radially inwardly extendingapertures in a radially outer surface of the carrier. Pins are thenmoved into the apertures to lock the fingers within the slots. The firstring gear half then is moved over the apertures.

In another embodiment according to any of the previous embodiments, thesecond ring gear half is placed on the intermediate gears subsequent tothe locking of the fingers within the slots.

In another embodiment according to any of the previous embodiments, thesun gear and intermediate gears are each formed as a single gear, andthe ring gear is formed.

In another embodiment according to any of the previous embodiments, thesun gear and the intermediate gears have two spaced portions. Each ofthe portions has helical gear teeth, with the helical gear teeth on thetwo portions extending in opposed directions. The two ring gear halveseach have one direction of helical gear teeth, with the helical gearteeth on the two ring gear halves extending in opposed directions.

In another embodiment according to any of the previous embodiments,journal bearings are inserted within each of the intermediate gearsprior to a first ring gear half being placed about the outer peripheryof the intermediate gears, and attaching a torque frame to the carrier.

In another featured embodiment, a gear reduction for use in a gasturbine engine comprises a unitary carrier centered on an axis andhaving a pair of axially spaced apart side walls, and axially extendingcircumferentially spaced connecting structure for connecting the pair ofspaced side walls. A central opening, and circumferentially spacedsmaller openings are spaced radially outwardly of the central opening.Internal surfaces of the circumferentially spaced curved walls defineintermediate gear pockets, with the intermediate gear pockets extendingaway from the central enlarged opening for a distance greater than adiameter of intermediate gears received in the intermediate gearpockets. Intermediate gears are received in the intermediate gearpockets, and secured at a position spaced radially inwardly of aradially outermost area in the intermediate gear pockets. Theintermediate gears have teeth engaged with teeth of a sun gear receivedin the central opening. A ring gear is received at radially outerlocations such that ring gear teeth engage teeth of the intermediategears.

In another embodiment according to the previous embodiment, theintermediate gears and the sun gear are formed of single gear bodies.The ring gear is formed of two separate ring gear halves. Theintermediate gears are secured by bushings. Journal bearings areinserted within each of the intermediate gears.

In another embodiment according to any of the previous embodiments, atorque frame has a plurality of axially extending fingers receivedwithin slots in the carrier, at locations circumferentially intermediateof locations of the intermediate gears. Pins inwardly of radiallyinwardly extend apertures in a radially outer surface of the carrier.The pins lock the fingers within the slot. The ring gear is receivedradially outwardly of the radially inwardly extending apertures.

In another embodiment according to any of the previous embodiments, thesun gear and the intermediate gears have two spaced portions. Each ofthe portions have helical gear teeth, with the helical gear teeth on thetwo portions extending in opposed directions. The two ring gear halveseach has one direction of helical gear teeth, with the helical gearteeth on the two halves ring gear extending in opposed directions.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a front portion of a gasturbine engine illustrating a turbo fan, epicyclic gear train and acompressor section.

FIG. 2 is a cross-sectional view of the epicyclic gear train shown inFIG. 1.

FIG. 3A shows a unitary carrier.

FIG. 3B is an end view of the epicyclic gear train taken along line 3-3in FIG. 2 with star gears shown in an installation position.

FIG. 4 is an enlarged view of a portion of the epicyclic gear trainshown in FIG. 3 with a sun gear and star gears shown in phantom.

FIG. 5 is an enlarged view of a portion of the epicyclic gear trainshown in FIG. 2.

FIG. 6 shows a feature of a gear.

FIG. 7A shows an assembly step.

FIG. 7B shows a subsequent assembly step.

FIG. 7C shown another subsequent step.

FIG. 7D shows a torque frame.

FIG. 7E shows a subsequent step.

FIG. 7F shows you another subsequent step.

FIG. 8 schematically illustrates a star gear being inserted into thecarrier.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath B whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 to drive the fan 42 at a lower speed than the lowspeed spool 30. The high speed spool 32 includes an outer shaft 50 thatinterconnects a high pressure compressor 52 and high pressure turbine54. A combustor 56 is arranged between the high pressure compressor 52and the high pressure turbine 54. A mid-turbine frame 57 of the enginestatic structure 36 is arranged generally between the high pressureturbine 54 and the low pressure turbine 46. The mid-turbine frame 57further supports bearing systems 38 in the turbine section 28. The innershaft 40 and the outer shaft 50 are concentric and rotate via bearingsystems 38 about the engine central longitudinal axis A which iscollinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle.The geared architecture 48 may be an epicycle gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.5:1. It should be understood, however, that theabove parameters are only exemplary of one embodiment of a gearedarchitecture engine.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFCT’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of[(Tram°R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” asdisclosed herein according to one non-limiting embodiment is less thanabout 1150 ft/second.

The geared architecture 48 may be assembled as described below for geartrain 122. In the example arrangement shown, the epicyclic gear train122 is a star gear train. Of course, the claimed invention also appliesto other epicyclic gear trains such as a planetary arrangement.Referring to FIG. 2, the epicyclic gear train 122 includes a sun gear128 that is connected to the compressor shaft 124, which providesrotational input, by a splined connection 130. A carrier 134 is fixed tothe housing 112 by a torque frame 136. The carrier 134 supportsintermediate gears (which are star gears 132 in the arrangement shown)that are coupled to the sun gear 128 by meshed interfaces 126 betweenthe teeth of the sun and star gears 128, 132. A ring gear 138A/Bsurrounds the carrier 134 and is coupled to the star gears 132 by meshedinterfaces 144. The ring gear 138A/B, which provides rotational output,is secured to the turbo fan shaft 120 by connection 142. Ring gear 138is actually formed by two ring gear halves 138A and 138B.

In one example, the torque frame 136 grounds the carrier 134 to thehousing 112. For example, mounts 154 have apertures 156 receivingfingers 230 of the torque frame 136, as shown in FIGS. 2 and 5. Pins 148extend through spherical bearings 146 and bushings 152 secure thefingers 230 to the carrier 134. Fasteners 150 retain the pins 148 to thecarrier 134.

The carrier 134 is a unitary structure manufactured from one piece forimproved structural strength and rigidity, as compared with two-parthousings, as shown in FIG. 3A. Carrier 134 is centered on an axis A (seeFIG. 4). The carrier 134 includes axially spaced apart side walls 160that are interconnected by the circumferentially spaced structuredefining mounts 154, which are generally wedge-shaped members, as bestshown in FIG. 3B. The mounts 154 and side walls 160 are unitary with oneanother. That is, these components are fixed, such as by being welded orcast as a unitary structure, before the gear train is assembled. Themounts 154 have opposing curved surfaces (see FIG. 3B) 158 that are inclose proximity to the star gears 132 and generally follow the curvatureof the teeth of the star gears 132 so that any oil on the curvedsurfaces 158 will likely find its way to the star gears 132 foradditional lubrication.

The mounts 154 are circumferentially spaced about the carrier 134 toprovide apertures 198 through which the star gears 132 extend to engagethe ring gear 138. The side walls 160 include holes 162 for receiving ajournal bearing 164 (see FIG. 2) that supports each of the star gears132. Each journal bearing 164 is retained within the carrier 134 byretainers 166 fastened to the side walls 160.

Oil baffles 168 are arranged between the side walls 160 near each of themounts 154, best shown in FIG. 2. Referring to FIGS. 4 and 5, thebaffles 168 include ends 172 that abut the mounts 154, in the exampleshown. The baffles 168 also include opposing curved surfaces 170arranged in close proximity to the star gears 128. The curved surfaces158, 170 are contiguous with and adjoin one another, in the exampleshown, and provide gear pockets 202 that receive the star gears 132. Agear pocket 204, which receives the sun gear 128, is also providedbetween a surface 173 on each of the baffles 168 opposite the ends 172.

As shown in FIG. 4, one of the side walls 160 includes holes 174 thatreceive fasteners 176 which secure each of the baffles 168 to thecarrier 134. The baffles 168 include a lubrication passage provided by aprimary passage 186 that fluidly communicates with a lubricantdistributor 178. The lubricant distributor 178 is fed oil from alubricant supply 196. In one example, the baffles 168 include openings182 that receive a tube 180 extending through a hole 183 in the sidewall 160. Seals 184 seal the tube 180 to the opening 182 and lubricantdistributor 178. Other tubes 192 having seals 184 are used to provideoil to an external spray bar 194 through another lubrication passage(spray bar passage 193 that extends through one of the baffles 168). Theexternal spray bar 194 is secured to the carrier 134 and sprays oil inthe vicinity of the sun gear 128 near the splined connection 130 (shownin FIGS. 2 and 5).

The primary passage 186 is in communication with first and secondpassages 188, 190 that spray oil on the teeth of the sun and star gears128, 132. In the example shown, the first and second passages 188, 190are arranged ninety degrees from one another.

With the example baffles 168, lubricant distribution is integrated intothe baffle so that separate components are eliminated. The baffles 168can be constructed from a different, lighter weight material than thecarrier 134.

The example carrier 134 is constructed from one piece, which improvesthe structural integrity of the carrier. A central opening 200 ismachined in at least one of the side walls 160 and provides the gearpocket 204, see FIG. 4. Gear pockets 202 are machined between the sidewalls 160 and mounts 154 for each of the star gears 132 and formapertures 198 at an outer circumference of the carrier 134.

Returning to FIG. 3B, the star gears 132 are inserted into the centralopening 200 and moved radially outwardly so that they extend through theapertures 198 and are preferably in abutment with the mounts 154(position indicated by dashed lines in FIG. 3B). This is schematicallyillustrated in FIG. 8. In this position, there is an adequate gap, t,between the teeth of adjacent star gears 132 to accommodate a width, w,of the end 172 of the baffles 168. After the baffles 168 have beeninserted, sun gear 128 can be inserted into the central opening 200. Thestar gears 132 can now be moved radially inwardly to mesh with the sungear 128. The baffles 168 are secured to the carrier 134 using fasteners176. The tubes 180, 192 can be inserted and the rest of the lubricantdistribution system can be connected.

As mentioned above, the star gears 132 are initially inserted within thecentral hole 200 for the sun gear. The star gears 136 are moved radiallyoutwardly, and the spray bars or baffles 168 are inserted. The sun gear128 is then inserted, and the star gears 132 may then be moved radiallyinwardly to engage the sun gear 128. All of this assembly occurs withthe carrier already formed as a unitary structure.

As shown in FIG. 6, the star gears 132 have two toothed portions, 302and 300, which have helical gear teeth extending in opposed directions.A central area 304 is formed between the toothed portions 302 and 300.Notably, the sun gear looks much the same. The two-part ring gear 138A/Bhalves each mate with one of the two gear teeth directions.

As shown in FIG. 7A, once the sun gears 128 and star gears 132 are inengagement, the journal bearings 164 may be inserted within the stargears 132. After this, as shown in FIG. 7B, a first half of the ringgear 138A may be moved onto the outer periphery of the star gears 132. Amanifold 210 may then be mounted to the gear as shown in FIG. 7C. Themanifold 210 has a fluid connection 212 which would be received within acentral aperture 214 in the journal bearings 164.

FIG. 7D shows a detail of a torque frame 136. As shown, fingers 230extend away from a plane of the torque frame. As mentioned above, thefingers 230 are received within the slots 156 in the unitary carrier134. The pins 148 may then be moved inwardly through the openings 220 inthe mounts 154 to lock the torque frame 156 to the carriers 134.

As can be appreciated in FIG. 7E, the ring gear half 138A has been movedaxially such that it does not line up with the apertures 220 in thecarrier, which is to receive the pin 148. Once the pin 148 has beenmoved inwardly to lock the finger 230 within the slot 156, then the ringgear half 138A may be moved back axially over a portion of the aperture220.

As shown in FIG. 7F, the next step is to mount the other ring gear half138B, completing the gear drive. At each step, all of the components aresecured in some manner. An oil gutter may then be installed.

The arrangement as set forth above thus provides a way to assemble anepicyclic gear train within a unitary carrier housing. Such a geartrain, configured and assembled as disclosed herein, has an improvedstrength and rigidity as compared with such a train having a two-partcarrier housing.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art would recognize that certainmodifications would come within the scope of this invention. For thatreason, the following claims should be studied to determine the truescope and content of this invention.

The invention claimed is:
 1. A method of mounting a gear train to atorque frame comprising: a) providing a unitary carrier having a centralaxis that includes spaced apart walls and circumferentially spacedconnecting structure defining mounts for interconnecting the walls,spaced apart apertures provided between the mounts at an outercircumference of the carrier, gear pockets provided between the wallsand mounts extending to the apertures, and a central opening in at leastone of the walls; b) inserting a plurality of intermediate gears and asun gear in the carrier; c) placing a first ring gear half about theouter periphery of said intermediate gears, and attaching a torque frameto said carrier; (d) mounting a second ring gear half to the outerperiphery subsequent to the torque frame being mounted to the carrier;and (e) inserting journal bearings within each of said intermediategears prior to step c).
 2. The method as set forth in claim 1, whereinsaid torque frame has a plurality of axially extending fingers which arereceived within slots in the carrier, at locations circumferentiallyintermediate locations of said intermediate gears, and said first ringgear half is moved such that it does not block radially inwardlyextending apertures in a radially outer surface of said carrier, andpins are then moved into said apertures to lock said fingers within saidslots, with said first ring gear half then being moved over saidapertures.
 3. The method as set forth in claim 2, wherein the secondring gear half is placed on the intermediate gears subsequent to thelocking of the fingers within the slots.
 4. The method as set forth inclaim 3, wherein said sun gear and intermediate gears are each formed asa single gear.
 5. The method as set forth in claim 1, wherein said sungear and said intermediate gears have two spaced portions, with each ofsaid portions having helical gear teeth, with said helical gear teeth onsaid two portions extending in opposed directions, and said two ringgear halves each have one direction of helical gear teeth, with thehelical gear teeth on said two ring gear halves extending in opposeddirections.